In the subsea exploration and production of oil and gas, installations are frequently located at the seabed with a plurality of guidelines extending upwardly from guide posts and coupled at sea level to a platform or vessel. These guidelines are used to lower or raise various equipment with connecting devices being coupled to the equipment and being slidable along the guidelines.
Due to the extreme environment of such subsea installations, these guidelines frequently break and must be immediately replaced to continue the subsea operations. To accomplish this replacement, it is advantageous to sever the broken guideline from the guide post from which it extends. In addition, this severance should be as close to the top of the guide post as possible to facilitate replacement.
However, there are two basic problems involved in cutting off the broken remnant of a subsea guideline. The first is the difficulty of remotely guiding a cutter mechanism to the exposed top of the guide post. The other is the difficulty of remotely positioning the guideline itself relative to the cutting mechanism.
In accomplishing this cutting of the broken guideline, the positioning of the cutting device adjacent to the top of the guide post is critical. Thus, it is typically necessary to make the cut as near as possible to the guide post top to minimize the remaining stub of the exposed guideline. This is necessary to facilitate attaching a new guideline with a latch mechanism.
In addition, the breaking of the guideline is random and unpredictable. The break might occur high above the guide post, resulting in a very long, limp pigtail. Often in such cases, the guidelines become crimped near the top of the guide post with a portion of the guideline extending downwardly along the side of the guide post, complicating both the problem of locating the cutting mechanism at the top of the guide post and the problem of positioning the guideline in the cutting mechanism. Alternatively, the break in the guideline may occur within one or two feet above the guide post top. Often in such cases, the guideline will fray into a multi-strand mare's tail, complicating both the problem of locating the cutting mechanism at the top of the post and the problem of positioning the guideline in the cutting mechanism.
While there are various devices for cutting subsea lines, not necessarily broken, and there are various prior art devices for cutting broken guidelines, these have numerous disadvantages. Thus, many of them are quite heavy and bulky, inconvenient to store on a platform or vessel at the sea level, and complicated to manufacture and operate. In addition, many of these devices are not accurately guided to the top of the guide post and do not sever the broken guideline at the required position immediately adjacent the top of the guide post. Finally, these devices do not efficiently handle the various different configurations of the broken guideline.
Examples of these prior art devices are disclosed in the following U.S. Pat. Nos.: 488,837 issued on Dec. 27, 1892 to Squires et al; 504,203 issued on Aug. 29, 1893 to DeBem; 541,018 issued on June 11, 1895 to Shryock; 756,760 issued on Apr. 5, 1904 to Wolf; 1,042,630 issued on Oct. 29, 1912 to Wetmore; 2,175,757 issued on Oct. 10, 1939 to Metzler; 2,825,536 issued on Mar. 4, 1958 to Kenneday et al; 3,036,522 issued on May 29, 1962 to Lindsey; 3,709,291 issued on Jan. 9, 1973 to Hanes et al; and 3,926,252 issued on Dec. 16, 1975 to Ribeyre et al.
Thus, there is still need for improvement in apparatus for and methods of cutting broken subsea guidelines.